What if the potential hire has an EAD card based on his green card process – should we still consider an H-1B COE case or can we employ him on the EAD?

This is a business decision for the company to make. Our firm and the USCIS recommend that a foreign worker maintain their nonimmigrant status (if possible) while completing the green card process. H-1B status provides the foreign worker more protections and is not tied to the green card process. For this reason, we normally recommend that an H-1B COE case be done rather than relying on an EAD card for work authorization. However we would need to review the specific facts on a case by case basis.
Please note that if an individual has already commenced employment using an EAD card based on the green card process, they are unable to resume H-1B status without jeopardizing the green card case.